Rodents can be a real annoyance and even a danger. These uninvited creatures consume everything, from vegetables to breadcrumbs, spreading bacteria and pathogens in the process. Rodents also cause major damage to stored crops and agricultural infrastructure. In areas where natural predators no longer occur, they become bold enough to venture out into orchards where they consume and carry away surprising quantities of crops.
They contaminate food and frequented areas with feces, urine, and hair. They carry diseases, such as spirochetal jaundice and murine typhus. According to the Centers for Disease Control and Prevention: Worldwide, rats and mice spread over 35 diseases. These diseases can be spread to humans directly, through handling of rodents, through contact with rodent feces, urine, or saliva, or through rodent bites. Diseases carried by rodents can also be spread to humans indirectly through ticks, mites or fleas that have fed on an infected rodent.
Getting rid of rodents can be a nuisance as well, to the earth, and to the health and safety of the indoor environment. Repellents may be used to non-lethally deter offending rodents. Current agronomic practices using exclusion such as wire fencing is limited in effectiveness and is expensive to apply. Poison bait is effective but limited to the area in which it is used and restricted in application because of non-target lethal effects. Both natural and chemical-based repellents are commercially available and vary in effectiveness. The smells of some plants, such as eucalyptus, wormwood and mint, are unattractive to rodents. However, they usually are minimally effective in repelling rodents.
Sound-based repellents are capable of emitting sound at a register too high for humans to recognize. These sounds are thought to be disconcerting to rodents and are intended to prevent them from infesting the area around them. However, sound-based repellents have shown limited effectiveness.
Repellents generally work by taking advantage of an animal's natural aversion to something, and often the thing chosen is something that the animal has learned to avoid (or instinctively avoids) in its natural environment. Chemical repellents mimic natural substances that repel or deter animals, or they are designed to be so irritating to a specific animal or type of animal that the targeted animal will avoid the protected object or area. Some chemical repellents combine both principles. Repellents fall into two main categories, odor and taste.
There remains a continued need for a reliable and economical method to non-lethally deter rodents from visiting uninvited locations or otherwise becoming a nuisance in such manner that neither the environment nor the rodents are harmed.